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From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: Passing the same actual as both in and out formal parameters?
Date: Tue, 17 Nov 2009 03:26:29 -0800 (PST)
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Date: 2009-11-17T03:26:29-08:00
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Jean-Pierre Rosen wrote on comp.lang.ada:
> Ludovic Brenta a =E9crit :
>
>  procedure P (A : in T; B : out T) is
>> begin
>> =A0 =A0B.L :=3D A.M; -- does this change A.L too?
> Yes
>> =A0 =A0B.M :=3D A.L; -- bug: A.L has been clobbered, now B.M =3D B.L?
>> end P;
>
>> My concern stems from the fact that T is tagged (I cannot change
>> that), so Object is passed by reference as both A and B.
>
>> Am I right to be concerned?
>
> Depend on what your concern is ;-)
> The semantic is well defined: tagged types are by-reference type. If you
> want to swap two fields of different parameters of the same type, use a
> local variable.

My exampled was heavily simplified; the actual type has about a
hundred components and the procedure P is a little more complex than
swapping components :)

But thanks for the responses, Niklas and Jean-Pierre. They confirm my
suspicion.

--
Ludovic Brenta.